Chemical breathing apparatus with alarm device

ABSTRACT

Chemical breathing apparatus for use by humans and adapted to supply life-sustaining gases to the respiratory tract of a human and having a canister carrying a chemical sorbent for treating the gases to be utilized by the human and an electrically actuated alarm device including means for measuring the resistance of the chemicals for giving a warning as to how much longer the chemical will be effective for treating gases and vapors in hazardous atmospheres.

United States Patent 1 1 Wallace NOV. 20, 1973 CHEMICAL BREATHINGAPPARATUS WITH ALARM DEVICE [76] Inventor: Richard A. Wallace, 43Kingscote Garden, Stanford, Calif. 94305 [22] Filed: Mar. 10, 1971 [21]Appl. No.: 122,658

[52] US. Cl 128/1416, 23/281, 55/275,

340/235 [51] Int. Cl. A62b 7/10 [58] Field of Search 128/1426, 203,146.2,

[56] References Cited UNITED STATES PATENTS 3,403,981 10/1968 Lemcke128/191 7/1964 Patrick 340/235 8/1965 Miller 128/1426 PrimaryExaminer-Richard A. Gaudet Assistant Examiner-G. F. DunneAttorney-Flehr, Hohbach, Test, Albritton 8L Herbert 5 7 ABSTRACTChemical breathing apparatus for use by humans and adapted to supplylife-sustaining gases to the respiratory tract of a human and having acanister carrying a chemical sorbent for treating the gases to beutilized by the human and an electrically actuated alarm deviceincluding means for measuring the resistance of the chemicals for givinga warning as to how much longer the chemical will be effective fortreating gases and vapors in hazardous atmospheres.

13 Claims, 10 Drawing Figures Patented Nov. 20, 1973 3,773,044

4 Sheets-Sheet 1-3 BREATHING TIME IN MINUTES F I g 4 INVENTOR Richard A.Wallace Patented Nov. 20, 1973 3,773,044

4 Sheets-Sheet 5 15/ INVENTOR.

Richard A. Wallace Attorneys Patented Nov. 20, 1973 3,773,044

4 Sheets-Sheet 4 INHALATION TIME IN MINUTES F i g I0 SWHO NI BONVLSISHUIVOIWBHO EXHALATION TIME IN MINUTES INVENTOR.

Richard A. Wallace z iforneys SWHO NI BQNVLSIS'HU 'IVOIWBHO CHEMICALBREATHING APPARATUS WITH ALARM DEVICE BACKGROUND OF THE INVENTION 1.Field of the Invention This invention relates to chemical breathingapparatus with an electrically actuated safety alarm device and moreparticularly to such chemical breathing apparatus in which theelectrically actuated alarm device measures the resistivity of at leastone chemical sorbent being utilized to ascertain when its resistivity isgreatly decreased upon the absorption of moisture or, alternatively,irritant gases and vapors sorbed by the chemical sorbents within thegas-filter apparatus.

2. Description of the Prior Art 7 Chemical breathing apparatus hasheretofore been provided. There are two types of chemical breathingapparatus: (1) the chemical oxygen-generating apparatus known as theChemox; and (2) the gas filter apparatus for protection against harmfuland irritant gases and vapors in contaminated atmospheres.

The oxygen-generating Chemox breathing apparatus utilizes a dialmechanical timer preset by the wearer. Such an indicator has been foundto be relatively unreliable because it merely gives an indication of thepassage of time and does not show the effective condition of thechemical sorbent in the canister. In addition, it has been found thatthe ringing of a bell alarm by the dial-timer often cannot be heard overthe noise in the encironment in which the breathing apparatus is beingused. It, therefore, can be seen that such prior indicating and warningmeans have very undesirable disadvantages.

Certain gas filter breathing apparatus has been provided with a windowindicator in the canister. Normally, in such a window indicator, twopieces of paper of different colors are located side-by-side in thewindow. One paper is treated chemically to change color as it absorbsmoisture. When it has changed sufficiently in color to match the paper,this should indicate that the chemical sorbent or chemical sorbents havelost or will shortly lose their effectivness. In order to make a properobservation of the colors, it is necessary that the window indicator beobserved in daylight. In addition, because of the position of the windowindicator, it is very difficult, if not impossible, for the wearer toobserve the indicator while the mask is being worn. There is, therefore,a need for a chemical breathing apparatus with new and improved alarmsafety means.

SUMMARY OF THE INVENTION AND OBJECTS The chemical breathing apparatus isfor use by humans and is adapted to supply life-sustaining gases to therespiratory tract of the human from a gaseous environment in which thehuman is present. The apparatus consists of a canister adapted to becarried by the human. The canister contains at least one chemicalsorbent for sorbing and/or neutralizing gases entering the canister andwhich will react with the chemical sorbent or chemical sorbents to treatthe gases so they are more suitable for use by a human. The chemicalsorbent or chemical sorbents undergo a progressive change as additionalgases pass through the chemical. A fact mask is adapted to makeconnection with the respiratory tract of the patient for supplying gasesto the respiratory tract of the patient. Means is connected to the facemask and to the canister for supplying gases passing through thecanister to the face mask. Electrically actuated safety means isprovided for giving an indication as to approximately how much longerthe chemical sorbent will be effective in sorbing and neutralizing thegases.

In general, it is an object of the present invention to provide achemical breathing apparatus which has an electrically actuated safetyalarm device for giving an indication as to how much longer the chemicalsorbent will be effective in sorbing, neutralizing and/or treating gasesto be utilized by the wearer.

Another object of the invention is to provide apparatus of the abovecharacter which gives a good indication of the remaining service lifefor the canister.

Another object of the invention is to provide apparatus of the abovecharacter which will light a lamp to give the warning or safety alarm.

Another object of the invention is to provide apparatus of the abovecharacter in which the lamp will remain energized for a substantialperiod of time after it is first energized.

Another object of the invention is to provide apparatus of the abovecharacter in which it is possible periodically to check or inspect theeffectiveness of the apparatus in storage.

Another object of the invention is to provide apparatus of the abovecharacter which will tell the wearer quite accurately while being wornthe remaining time during which the apparatus will be effective.

Another object of the invention is to provide apparatus of the abovecharacter in which there is given an indication which is a directmeasure of the amount of remaining unused chemical sorbent in theapparatus.

Another object of the invention is to provide apparatus of the abovecharacter in which the alarm device is relatively inexpensive and can beeasily manufactured.

Another object of the invention is to provide apparatus of the abovecharacter in which the alarm device is very reliable.

Another object of the invention is to provide an alarm device of theabove character which can be adapted to apparatus already in the field.

Additional objects and features of the invention will appear from thefollowing description in which the preferred embodiments are set forthin detail in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a front elevational view of achemical oxygen-breathing apparatus with an electrically actuated alarmdevice incorporating the present invention.

FIG. 2 is a cross-sectional view taken along the line 22 of FIG. 1.

FIG. 3 is a circuit diagram of the electrically actuated alarm deviceutilized in the embodiment shown in FIGS. 1 and 2.

FIG. 4 is a graph showing the chemical resistance of the chemicalsorbent utilized in a typical oxygen generating chemical breathingapparatus plotted against exhalation time in minutes.

FIG. 5 is a front elevational view of a fireman wearing a chemicalgas-filter breathing apparatus with an electrically actuated alarmdevice incorporating another embodiment of the invention.

FIG. 6 is a cross-sectional view taken along the line 6-6 of FIG. 5.

FIG. 7 is a circuit diagram of the electrically actuated alarm deviceutilized in the embodiment shown in FIGS. and 6.

FIG. 8 is an isometric view in cross-section of a canister with anotherembodiment of the electrode means.

FIG. 9 is a graph showing the electrical resistance of a chemicalsorbent in a typical gas-filter breathing apparatus plotted againstexhalation time.

FIG. 10 is a graph showing the electrical resistance of a chemicalsorbent in a typical gas-filter breathing apparatus plotted againstinhalation time.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The chemical oxygen breathingapparatus with an electrically actuated alarm device is for use byhumans and is adapted to supply lifesustaining gases to the respiratorytract of the human while the human is operating in a gaseousenvironment. The apparatus includes a canister 11 which consists of ashell 12 formed of a suitable material such as copper-plated steel. Theshell 12 can be in the form of a deep-drawn receptacle or body 13 havinga bottom open end which is closed by a bottom wall 14 that is secured tothe body 13 by a seam 16. The receptacle or body 13 is provided with anopen neck 17 at its upper end. An openended tube 18 extends downwardlyinto the shell 12 from the neck 18 as shown particularly in FIG. 2. Thetube 18 is formed of a suitable material such as copper.

A suitable oxygen-evolving chemical sorbent 21 is provided within theshell 12. This chemical 21 fills most of the space within the shell 12as also shown in FIG. 2. One chemical sorbent found to be particularlysatisfactory is potassium superoxide. The lower portion of the chemicalcan be impregnated with a catalyst to speed the chemical reaction togenerate oxygen.

A space 22 is provided beneath the chemical and at the bottom of thecanister to permit circulation of the incoming breath through thechemical and to ensure minimum breathing resistance. Filters 23 areprovided above and below the chemical and at the top and bottom of thecanister to prevent tiny particles of the chemical from entering thebreathing system of the human while the canister is being used.Yieldable means in the form of a spring 24 below the lower filter 23urges the filter 23 upwardly to provide a space 25 below the lowerfilter 23 so that air passing through the tube 18 will be distributedover the entire exposed surface of the lower filter 23. When not in use,the canister is hermetically sealed to prevent air from coming intocontact with the chemical sorbent within the canister.

The canister 11 is adapted to be inserted into a har ness assembly 26.The harness assembly 26 consists of a rigid backing plate or frame 27that has an insulated canvas covering 28 mounted on the same which isopen at the bottom end and which is adapted to receive the canister 11.The harness assembly also includes upper and lower straps 29 and 31which are adapted to encircle the body of the human user to hold theframe 27 against the front of the body of the user. In addition, thereis provided another strap 32 which is secured to opposite sides of theframe 27 as shown and which is adapted to pass over the shoulders andback of the neck of the user. A U-shaped bracket 33 is pivotally mountedupon the covering 28 and is adapted to swing below the covering 28 asshown in FIG. 1. A screw 34 is threaded into the bracket and is providedwith a knob 36. A plate 37 is mounted on the screw 34 and is adapted toengage the bottom of the canister.

A plunger assembly 41 is mounted upon the canister holder or covering 28and includes a spring-located plunger (not shown) mounted within ahollow housing. The plunger is in the form of a cylindrical tube with acone-shaped tip that is adapted to pierce an exposed copper foilprovided in the neck 17 of the canister when the canister 11 is thrustupwardly against it by the force of the screw 34 operated by the user.The tip of the plunger is perforated to allow the exhaled breath of theuser to enter the canister. The plunger in the form of the cylindricaltube communicates with the tube 18 provided within the canister so thatthe exhaled breath of the user will pass through the canister ashereinafter described.

Means in the form of a face piece assembly 46 is adapted to make aconnection with the respiratory tract of the patient or user. The facepiece assembly consists of a face mask 47 formed of suitable materialsuch as rubber which is adapted to fit over the face of the user andform an air-tight seal therewith. The mask is provided with a strapassembly 48 for securing the mask to the head of the user. The mask isprovided with lens 49 to give the user visibility through the mask. Themask is fitted with a mouthpiece assembly 51 to permit the wearer tocarry on a communication while wearing the face piece assembly 46. Amanifold assembly 52 is also connected to the face piece assembly by apair of tubes 53 and 54. An exhalation valve (not shown) is mounted inthe lefthand side of the manifold assembly 52 and is adapted toestablish communication with an exhalation breathing tube 56 that isconnected to the plunger assembly 41 as shown in FIG. 1. The right-handside of the manifold assembly 52 is provided with an inhalation valveassembly (not shown) which is adapted to establish communication with aninhalation breathing tube 57 that is connected to a breathing bag 58.The manifold assembly 52 is also provided with a relief valve (notshown).

The breathing bag 58 is in the form of an inverted U and is secured tothe canister frame or backing plate 27. An inlet tube 59 is provided onthe right-hand side or lobe of the breathing bag 58 and is incommuncation with the inhalation breathing tube 57. An outlet tube 61 isprovided in the other or left-hand side or lobe of the breathing bag andis in communication with the outer housing of the plunger assembly 41and with the interior of the canister 11 as shown particularly inFIG. 1. A timer 62 is carried by the canister frame. The timer isactuated by twisting a pointer 63 clockwise as far as it will turn. Thisautomatically sets a bell to ring after 45 to minutes as desired.

A name plate holder 65 is secured to the canister holder 28 and carriescertain instructions.

The portion of the chemical breathing apparatus thus far described isconventional and is known under the trademark Chemox and is supplied byMine Safety Appliances Company of Pittsburgh, Pa.

Means has been provided as a part of the chemical breathing apparatus inthe form of electrically actuated alarm means for indicatingapproximately how much longer the apparatus will be effective insupplying treated life-sustaining gases to the respiratory tract of theuser. Such means consists of a pair of electrodes 66 and 67 in which theelectrode 66 is in the form of a copper wire 68 which is covered with alayer 69 of a suitable insulating material. The copper rod or wire 68can be of a suitable size such as 8 or 10 gauge. The insulation 69 forthe copper wire can be of any suitable type which will withstand hightemperatures. For example, the insulation can be formed of a polymerwhich will withstand temperatures of 100C. continuously. It is necessarythat the insulation be able to withstand such a temperature because thechemical reaction which takes place during operation of the breathingapparatus is exothermic and generates a large amount of heat. Theelectrode 66 is positioned relatively precisely within the canister. Inparticular, it is positioned sufficiently far away from the side wallsof the canister so that an appropriate resistance is developed betweenthe two electrodes before the canister has been used. In addition, ashereinafter explained, the electrode 66 is positioned and has a lengthso it extends to a predetermined depth within the chemical sorbent 21.It can be readily appreciated that the greater the depth of penetrationof the chemical by the electrode, the sooner the visual indicator willbe energized. As can be seen from FIG. 2, the electrode 66 extendsdownwardly into the chemical 21 for a substantial distance and the tipof the same is free from insulation as shown in FIG. 2 and is exposed tothe chemical sorbent.

The electrode 66 extends through an insulator 71 mounted in the top wallof the canister and is connected to a terminal 72. The other electrode67 is the copper-plated canister itself. A connector 73 makes electricalcontact with the copper plating on the canister and is connected to aterminal 74 for engaging the terminals 72 and 74 and consists ofsnap-like connectors 76 which snap over the top of the terminals 72 and74 and which are carried by a flexible carrying ring 77. Wires 78 and 79are connected to the connector 76 and form a part of a cable 81. One endof the cable 81 is connected to the socket 82 which carries a bayonettype lamp 83. The socket 82 with the lamp 83 are mounted in a bracket 84which is secured to an alligator type clip 86. The clip 86 is adapted toclip onto any suitable part of the apparatus so that the lamp 83 can bereadily viewed by the user of the apparatus. Thus, as shown in FIGS. 1and 2, the clip 86 can be secured to the face mask 47 adjacent one ofthe lenses 49 so that when the lamp is lit, it will be readily noticedby the user of the apparatus. The other end of the cable is connected tosnap-like connectors 87 also carried by a flexible ring or loop 88. Theconnectors 87 are adapted to be secured to the terminals 89 of a battery91. The battery 91 is of a suitable type which is adapted for operatingwith the circuitry hereinafter described and for lighting the lamp 83.The battery 91 is removably secured in a spring-like bracket 92 whichpermits the battery to be readily inserted and removed. The bracket 92is provided with a hook 93 which is adapted to hook over the plate 63.

A circuit diagram of an electrical circuitry is shown tus in conjunctionwith the electrically actuated alarm device may now be briefly describedas follows. The chemical breathing apparatus can be donned by the userin a conventional manner. Thus, the straps 29, 31 and 32 can be put inplace. A canister 11 can be inserted in the canister holder 28 andpunctured by the plunger assembly 41 as hereinbefore described.Normally, the electrically actuated alarm system is already mounted onthe breathing apparatus. However, if not, it can be readily mounted onthe chemical breathing apparatus by placing the battery 91 with itsbracket 92 on the canister holder 28. The snap connectors 87 can beconnected to the terminals of the battery and similarly the snapconnectors 76 can be connected to the electrodes 72 and 74. The lamp 83can then be clipped in the desired position such as mounting the same onthe mask 47 adjacent one of the eye pieces 49 or, alternatively, on themouth-piece assembly 51.

The user is now in a position to don the face mask 47 whenever requiredas, for example, when entering a building which is on tire. The chemicalbreathing apparatus in this case is a self-generating oxygen breathingapparatus which operates independently of ambient air. The canistercontains a chemical sorbent which upon contact with the moisture in theexhaled breath generates oxygen to meet the breathing requirements ofthe user and also absorbs exhaled carbon dioxide from the exhaled air ofthe user. In use of the breathing apparatus, the air travels in the pathindicated by the arrows shown in FIG. 1. Thus, it passes downwardlythrough the exhalation tube 56 into the tube 18 and down and outwardlythrough the bottom of the tube into the space 25 where any increase inpressure is distributed uniformly, after which the air passes throughthe chemical 21 where the carbon dioxide is removed and the moisture inthe air reacts with the chemical to generate oxygen.

Potassium superoxide is activated by moisture in the breath, liberatesoxygen and produces potassium hydroxide which then reacts immediatelywith the carbon dioxide to form potassium bicarbonate. The gases passingthrough the canister thus have the carbon dioxide removed and haveoxygen added which travels upwardly through the exterior of the housingof the plunger assembly 41, through the tube 61, into one lobe of thebag 58, after which it is distributed uniformly throughout the bag andenters the tube 59 and passes through the inhalation tube 57 into theinhalation valve assembly and then into the face piece 47, after whichit enters the respiratory tract of the user through either the mouth orthe nose of the user. The removal of carbon dioxide from the exhaled airand the generation of oxygen by the canister provides a supply oftreated life-sustaining gases for the user from the recycled exhaledair. It can be appreciated that moisture from the exhaled air isabsorbed by the chemical sorbent in the canister. The moisture is firstabsorbed by the bottom portion of the chemical and then the moisturetravels upwardly as the bottom or lower portion of the chemical withinthe canister becomes saturated.

When the chemical within the canister has been approximately 2/3 to 3/4utilized, the moisture from the exhaled air will begin to reach theelectrode 68 which causes the chemical to serve as an electrolytewhereby electricity will begin to flow between the electrodek under theinfluence of the potential applied across the electrodes by the battery91. When the chemicalsorbent 21 is dry, its resistance is very high as,for example, several million ohms. The resistance decreases as theamount of moisture in the chemical increases. The resistance alsodecreases as the moisture absorption takes place because of the increasein temperature of the chemical sorbent caused by heat generated by theexothermic heat of absorption reaction. A curve which is representativeof the drop in resistance in the chemical sorbent, potassium superoxide,plotted against breathing time is shown in H6. 4. As can be seen fromFIG. 4, the resistance drops relatively rapidly with time so that afterapproximately 25 minutes, a minimum resistance of slightly below 10,000ohms is reached. At this point, the resistance is a minimum. Slightlyabove this lowermost point as determined by the parallel resistor 96,the current flow is sufficient to light the lamp 83. Once the lamp 83 islit, it will remain lit for a substantial moisture period of time. Itwill be noted from the curve shown in FIG. 4 that after a period of timethe resistance begins to increase gradually. It is believed that this isdue, in part, to the fact that gradually more and more of the chemicalsorbent has reacted with the moisture and also, in part to a decline intemperature of the potassium superoxide sorbent within the hot canister.

The user of the apparatus knows as soon as the light has come on that heonly has a limited period of time left during which the chemicalbreathing apparatus will supply him with sufficient oxygen. This,therefore, gives a warning to the user that he has only a very limitedperiod of time as, for example, minutes before he must leave the area.Within a very short period of time thereafter, the chemical breathingapparatus will fail because it will supply insufficient oxygen tosupport human life. In other words, the chemical will all be used up orreacted.

This electrically actuated alarm means can be the sole warning means orit can be supplemental to the mechanical timer alarm 62 which isprovided with the chemical breathing apparatus. It can be appreciatedthat in tires where there is a great deal of smoke and a lack of lightand also because of noise, a wearer of the chemical breathing apparatusmay be unable to read or hear the timer type alarm 62. In addition, thetimer 62 would not give an accurate indication of the amount of timethat is actually left in the remaining chemical sorbent in the canister11. The electrically actuated alarm means gives a much more accurateindication of the chemical sorbent remaining because the electricallyactuated alarm means will not be operated until a predetermined portionof the chemical has been utilized as determined by the depth of theelectrode 66. The wearer of the chemical breathing apparatus will immediately become aware when the lamp 83 is lit because it is in front ofthe eye piece or lens 49. Thus, the user will receive an alarm eventhough he may be in an environment in which there is very little or nolight and in which there is a great deal of noise. In the event that thewearer is overcome in such a situation, the lamp 83 will also indicateto rescuers the location of the user.

By way of example, in one embodiment of the apparatus, the resistor 96had a value of 180,000 ohms. The lamp was an NE-6'7 neon bulb. Thebattery 91 had a suitable voltage output such as 67% volts. Theadjustable resistor simulates the chemical sorbent 21 in the canister11. it was found that when the resistance of the chemical 21 in thecanister was reduced to approximately 19,000 ohms as set by the parallelresistor 96,

the lamp 83 was lit to give the indication of the impending exhaustionof the oxygen generation. As pointed out previously, the time requiredbefore the lamp will be lit can be adjusted by positioning of theelectrode 66. In addition, it can be adjusted by the voltage on thebattery 91 and it also can be changed by the value of the parallelresistance 96. As the parallel resistance is increased, the neon lamp 83will be fired at a lower resistance and after a greater period of time.By way of example, when the resistance 96 had a value of 180,000 ohms,the lamp 83 fired at 12,000 ohms and had a period of use by the wearerof approximately 21 minutes. With this resistor, the light remained onafter the canister was completely used up. When the resistance 96 wasreduced to 120,000 ohms, the lamp fired at 8,000 ohms or afterapproximately 30 minutes of use by the wearer. The light remained on fora pierod of ap proximately 40 minutes.

It should be appreciated that other means than that shown can beutilized for connecting the battery to the lamp and to the electrodes.

Thus, it can be seen that the lamp 83 serves as electrically actuatedalarm means which has many advantages over the mechanical timer typealarm 62 previously provided. It is relatively light and compact andmerely requires the use of a power supply in the form of a battery and apair of electrodes. Such alarm means is relatively simple and gives avery positive indication of the impending exhaustion of oxygengeneration by the can ister. The alarm means can be readily removed fromthe apparatus if desired.

The pushbuttom 97 is provided for testing the electrical circuitry to besure that it is operative before the wearer goes into a hazardouslocation.

Another embodiment of the chemical breathing apparatus is shown in FIGS.5 and 6 and is typically called the Universal All-Service Model Type Nwhich utilizes a filter type canister 101. This filter canister isgenerally a conventional type such as supplied by Mine Safety Appliancesof Pittsburgh, Pa; by Wilson Products Div. of Electric Storage Battery,lnc., Reading, Pa.; and by Acme, Inc., Pittsburgh, Pa. The canister 101consists of a drawn steel oval-shaped body 102 which has beencopperplated. A bottom closure wall 103 is provided for closing the openend of the body 102 and is connected to the body 102 by a seam 104. Aplurality of chemical sorbents are provided within the canister 10] andare arranged in layers in the canister 101. Thus, there is provided alarge layer 106 formed of Hopcalite which acts as a catalyst to convertcarbon monoxide to carbon dioxide by uniting the oxygen in the air tothe carbon monoxide thus forming carbon dioxide which is a relativelyharmless gas. The Hopcalite also has considerable absorbing powers fororganic vapors and acid gases. Screens 107 and 108 are provided aboveand below the Hopcalite layer 106. A suitable drying agent 109 ispositioned immediately above the Hopcalite and is formed of a suitablematerial such as pure anhydrous calcium chloride and serves to preventmoisture from reaching the Hopcalite from the top side. Another screen111 is provided above the drying agent 109 and a high efficiency filter112 is provided above the screen 111. A molecular sieve 113, such assilica gel, is positioned below the screen 108 and serves as an absorberof ammonia and also as a drying agent to prevent moisture from reachingthe Hopcalite. A screen 114 is provided below the molecular sieve 113.

A caustite layer 116 is provided below the screen 114 and is a soda limewhich is a mixture of caustic soda (NaOI-I) plus lime [Ca(OI-I) A screen117 is provided below the layer 116 and a layer 118 formed of activatedcharcoal is provided for absorbing organic vapors. A screen 119 isprovided below the layer 118. An ultra high efficiency filter 120 ismounted in the bottom of the canister and is provided for filteringtoxic dust, fumes, mist, fogs and smokes including radioactiveparticulates. The bottom closure member 108 is provided with an opening121 which is sealed when the canister is not in use to permit outsideambient air to enter. A spring 122 is provided in the upper end of thecanister for holding the chemical layers in position in the canister.The canister 101 is provided with a window indicator which warns theuser when the canister is no longer effective against carbon monoxide.

The body 102 of the canister is provided with a neck 122 which isadapted to be connected to the lower end of a flexible breathing tube123 by a coupling 124. The upper end of the tube 123 is connected to aface piece assembly 126 by a coupling 127. The face piece assembly isprovided with a mouthpiece assembly 128. It is also provided with a lens129 which provides panoramic vision to the user of the apparatus. Theface piece is adapted to be secured to the head of the wearer by a strapassembly 131. A harness assembly 132 is provided for mounting thecanister 101 on the front of the wearer and includes a strap 133 adaptedto be secured about the waist of the wearer as shown in FIG. and a strap134 adapted to extend over the shoulders of the wearer and behind theneck of the wearer.

The portion of the chemical breathing apparatus thus far described inconjunction with FIGS. 5 and 6 is conventional. However, with thepresent invention, electrically actuated alarm means is also providedfor giving an indication as to how much longer the canister will beeffective for treating the gases which are to be utilized by the weareror user. Such means takes the form of a pair of electrodes in which oneof the electrodes is in the form of a rod 141 that is mounted in thecanister and extends downwardly into the chemical sorbents in thecanister. The other electrode is the body 102 and the bottom closure 103of the canister which is provided with a ground lug 142. The rod 141 isin the form of 8 or gauge copper wire 143 covered by a layer 144 of hightemperature insulation of a suitable type such as a polymer. The rod 141extends to a suitable depth within the chemicals and, as shown in FIG.6, the insulation from the wire 143 is removed in two locations toexpose two portions 143a and 143b of the wire 143. The bare portion 143ais in the drying layer 109 immediately above the Hopcalite layer and theportion 143b is disposed in the caustite layer. The rod 141 is mountedon a terminal 146 which extends through the top wall of the body 102 ofthe canister 101. A clip 147 is secured to the terminal 146 and anotherclip 148 is secured to the ground lug 142. The clips 147 and 148 areconnected by wires 149 and 151 to a small power supply 170. The powersupply 150 consists of a housing 152 which can be clipped to the harnessassembly 132 as shown in FIG. 5. The printed circuit board 153 ismounted within the housing and is connected to a battery 154 carried bya clip 156 within the housing. The printed circuit board 153 and thebattery 154 are connected by conductors 157 and 158 to a lamp socket 159which is mounted upon a clip 161. A lamp 162 is mounted within thesocket 159 and is of a suitable type such as a 6 volt incandescent lamp.The clip 161 is adapted to be secured in a location so that the lamp 162can be readily viewed by the user of the apparatus. Thus, as shown inFIGS. 5 and 6, the clip has been secured to the brim of a helmet 164 sothat the lamp is clearly visible to the wearer. It also should bereadily apparent that the clip can be readily secured to other parts ofthe apparatus where it would still be readily visible to the wearer.

The circuit which is utilized for energizing the lamp 162 is shown inFIG. 7 and is mounted on the printed circuit board 153. The circuitincludes a resistor 166 that represents the variable resistance of achemical sorbent in the canister and a fixed resistor 167 having apredetermined value approximately 4 6 times as great as the resistanceof the chemical sorbent to provide resistance ratios ranging from 4 to 1to 6 to l. The junction between the two resistors 166 and 167 isconnected to the base of a transistor Q1. The emitter of the transistorQ1 is connected to the base of a transistor Q2. The collector of thetransistor Q1 is connected to one side of the lamp 162 and to thecollector of the transistor Q2. The emitter of the transistor Q2 isconnected to one side of the resistance 167.

There is provided a pushbutton 171 in series with a fixed resistor 172of a suitable value such as 5000 ohms which are in parallel with theresistance 166 representing the canister for testing the circuit to seewhether or not the circuit is operative and also to ascertain whether ornot the lamp 162 can be energized by the circuit.

Operation and use of the chemical breathing apparatus may now be brieflydescribed as follows. The chemical breathing apparatus can be donned bythe wearer in a conventional manner as shown in FIG. 2. The seals (notshown) are removed from the neck of the canister 101 as well as from theopening 121 in the bottom of the canister so that air can passtherethrough. The user can then press the pushbutton 171 to be sure thatthe circuit is operative. The clip 161 is secured at a convenientlocation and the face piece is then placed over the head of the user.The user is then in a position to enter the zone in which he desires toutilize the chemical breathing apparatus. During inhalation by thewearer of the apparatus, air enters the opening 121 in the bottom of thecanister 101 and passes into the interior. The air is thoroughlypurified, first by the filter 119, and through the various other layersof chemical sorbents in the canister, and then through the filter at thetop, through the breathing tube 123 into the face piece, and thence intothe respiratory tract of the user. The air in passing through thecanister is thoroughly purified by the filters which remove the largeparticle size dust, fumes, mists, fogs and smoke. The layers ofchemicals absorb or chemically neutralize harmful gases and vapors.

During exhalation, the air is expelled from the face piece through theexhalation valve 128 which, because of its location and design, permitsconversation between the wearer and others. It also serves as a drainfor moisture which may condense from the breath on the face piece. Acheck valve (not shown) fitted at the top of the canister preventsexhaled air from reentering the canister and being rebreathed.

The Hopcalite causes the carbon monoxide to oxidize to carbon dioxide byflameless combustion or catalysis. Thus, the canister will gen noticablyhot in the presence of carbon monoxide, in proportion to the amount ofgas passing through the canister. Generally, filter canisters of thistype are for respiratory protection against a specific gas or group ofgases which the canister is designed in areas where there is sufficientoxygen to sustain life 16 percent by volume) and where the total toxicgas concentration does not exceed 2 percent volume.

Some of the chemicals utilized in such filter canisters are particularlyhygroscopic and rapidly become ineffective when they come in contactwith moisture. The electrically actuated alarm system which iis providedas a part of the chemical breathing apparatus is provided for sensingaccumulation of moisture in the canister. When the chemicals are dry,the resistance is very high. The moisture begins to penetrate thechemicals from the bottom and gradually moves upwardly in the chemicalsas the chemicals on the bottom become saturated. At the time themoisture reaches the bottom exposed portion 1415b of the electrode 141,the resistance of the chemical will decrease very rapidly to permitoperation of the battery-operated transistor switch transistors Q1 andQ2 and to energize lamp 162. The transistor Q1 can be of the 2N3565 NPNtype. It is a small signal sili con, high gain transistor. Thetransistor Q2 can be TIP31A NPN silicon power transistor. The twotransistors Q1 and Q2 act as a voltage operated switch. Whenever thecontrol voltage across the resistor 167 sees the firing voltage of thetransistor switch (approximately 1.4 volts), then the transistor switchturns on thereby allowing current to flow through the lamp 162. Thus,the decrease in chemical sorbent resistance 166 within the canister willtend to increase the voltage developed across the fixed resistor 167,thus turning on the lamp 162. The energization of the lamp 162 willfirst be seen as a red wire glow which will gradually be transformed toa bright light as the resistance is decreased between the portion 143aand the canister and the circuit is completed through the groundterminal 142. The energization of the lamp 162 will be immediatelyvisible to the wearer and will warn him that he only may have a certainamount of effective time for the filter cansiter. This will indicate tohim that he must plan to leave the area in sufficient time so that thecanister will remain effective until he is able to reach a safe area.

An exposed portion 143a is also provided on the electrode 141 and isprovided for the purpose in the event the wearer becomes sick to hisstomach and vomits, or when the wearer erroneously attaches a differentmanufacturers breathing tube to another manufacturers canister, or forsome reason moisture comes through the neck of the canister and startspenetrating the chemical sorbent from the top. As soon as moisture isabsorbed by the chemicals, this will be detected by the exposed portion143a and a circuit can be established through the chemical sorbentserving as an electrolyte to the side wall of the canister and to groundto activate the transistors Q1 and O2 to again energize the lamp 162.This again will warn the wearer that he only has a certain amount oftime before the moisture will penetrate down to the Hopcalite and thuswarns him that the canister will only be effective for a certain periodof time so that he again must leave the area and be in a safe placebefore the breathing apparatus becomes ineffective.

By positioning the electrodes in the desired location in the chemicalsorbent, it is possible to program into the electrically actuated alarmsystem a predetermined amount of time after which the breathingapparatus will no longer be effective. It is important to note that thiselectrically actuated alarm system is directly responsive to the workfunction which is placed on the apparatus by the user himself and thusgives a much more accurate indication as to how much longer thebreathing apparatus will be effective in treating the gases. This istrue because the harder the breathing apparatus is worked by the wearer,the more mosture as well as harmful gases will be brought into thecanister filter.

In addition, the alarm device is very effective to give an accuratewarning when the breathing apparatus is being utilized in a damp orsteamy atmosphere. In such conditions, more moisture will be broughtinto the canister and the breathing apparatus will be effective for ashorter period of time. This will be indicated by the alarm device.

The types of construction which are shown in the previous embodimentsare types in which the alarm device can be incorporated in existingbreathing apparatus. This can be readily accomplished merely byinserting an electrode through the top wall of the canister and bymaking an appropriate ground connection.

When it is desired to incorporate the alarm device as a part of thebreathing apparatus when the breathing apparatus is being manufactured,a construction of the type shown in FIG. 8 or FIG. 6 can be utilized.

In FIG. 8 there is shown another embodiment of the electrodes for use inelectrically actuated alarm devices of the type shown in FIG. 6 andutilized with a canister generally of the type shown in FIG. 6. As showntherein, the terminal 146 is connected to an insulated wire 176 which isconnected at 177 to an additional conducting screen 178 which ispositioned in the middle of the layer 109 between the screens 107 and111 and generally parallel to the same. Another wire 181 is connected tothe wire 176 and is connected to another additional screen 182 at 183.The screen 182 is positioned in the middle of the layer 116 parallel tothe screens 114 and 117. It can be seen that the two conducting screens178 and 182 are disposed above and below the Hopcalite layer 106 and areconnected in parallel to the terminal 146.

With this type of construction, it can be seen that the wires can besecured to the additional screens 178 and 182 and the screens insertedduring assembly of the canister at the manufacturing plant.

The operation of this embodiment of the invention is very similar tothat hereinbefore described. The two screens 178 and 182 connected inparallel serve as one of the electrodes, whereas the canister itselfserves as the other electrode to which the grounding strap 142 issecured. The screens 178 and 182 are positioned in such a manner thatthey are above and below the Hopcalite and, therefore, will detect thepresence of moisture in the chemicals they are in contact with. Thus,the screens will sense the presence of moisture coming from eitherdirection above or below the Hopcalite. When the resistivity of thechemicals in which the screens 178 and/or 182 is reduced sufficiently,the lamp 162 will light to indicate to the wearer that there is only acertain amount of effective time left in the filter canister.

With the construction shown in FIG. 8, it can be seen that very littlecost will be added to the canister in providing the electrodes in theform of the screens 178 and 182 and the connecting wires for theelectrically actuated alarm means.

In FIGS. 9 and 10 are shown representative results which can be obtainedwith an electrode system of the type shown in FIG. 8. FIG. 9 shows thecurve which was obtained utilizing a Mine Safety Appliances Model SWAll-Service Filter Canister in which a copper mesh probe having a sizeof 1% inch by 2% inches was inserted in the middle of the anhydrouscalcium chloride layer 109. During the test, the check valve whichprevents exhaled air from reentering the canister was removed from thetop of the canister. Continuous heavy exhalation by the user into thecanister created the curve which is shown in FIG. 9. From the curve, itcan be seen that the resistivity remained relatively high forapproximately 40 minutes and then it dropped very sharply toapproximately 10,000 ohms. This served to indicate that the moisturepenetrated to the level of the screen which made the calcium chlorideextremely conductive so that the resistance dropped. The resistivityremained at this level for a considerable period of time as can be seenfrom the curve and thus once the light was energized, it remained on. Bythe abruptness of the drop in the resistance, it can be seen that thescreen electrode is very sensitive in sensing the penetration ofmoisture into the calcium chloride sorbent.

In another test of the invdntion which is shown in FIG. 10, the sametype of canister as was used in FIG. 9 was utilized. The copper screenconductivity probe /z inch by 2% inches in size was inserted in themiddle of the anhydrous soda lime (caustite) layer. In this case,exhaled air was introduced through the bottom of the canister by heavybreathing. It can be seen that the resistance remained very high forapproximately 50 minutes and then dropped very sharply to slightly over10,000 ohms again indicating that as soon as the moisture reached thescreen conductivity probe, the conductivity was quite good and thecircuit was operated to energize the lamp 162. As can be seen, theresistance thereafter remained relatively constant so that the lamp 162remained energized.

It should be apparent that the resistivity values are dependent upon anumber of factors, for example, the separation of the electrodes; thelength and size of the electrode mesh are also important factors.

In any event, it can be seen that the electrically actuated alarm deviceis very effective as a safety device and gives a very accurateindication as to the remaining effective life of the canister.Repeatable results can be readily obtained so that the alarm device canbe considered to be reliable.

The present invention is also useful in connection with gas filtercanisters for sorbing acid and basic irritable gases such as acidicchlorine (C1 bromine (Br sulphur dioxide (S hydrogen sulphide (Hhydrochloric acid (I-lCl), sulphuric acid (H 80 phosgene (COCI sulfurylfluoride (SO F sulfuryl chloride (SO CI and basic ammonia (NI-i andorganic amines. It has been found that the present invention is usefulfor such filter canisters because the chemical sorbents which areutilized have their values of electrical resistance decrease upon theabsorption of moisture and/or upon the absorption of acidic or basicgases or vapors. The absorption of moisture is not absolutely essentialsince the electrical resistance will decrease with only absorption ofacid or basic gases or vapors.

Thus, the same type of safety device as herein disclosed in conjunctionwith the previous embodiments can be utilized with such filter canistersto obtain the same mode of operation and to thereby provide anelectrically actuated alarm device which is very effective as a safetydevice and gives a very accurate indicationas to the remaining effectivelife of the canister. Certain representative tests utilizing canistersof this type will be set forth below.

A Mine Safety Appliance Model GML canister, filled with chemicalsorbents consisting of layers of soda lime and activated charcoal, wasused for protection against irritable chlorine vapor. The electrodewhich was inserted into this canister had exposed portions in the twosoda lime or caustite layers. Before use of the canister, it was foundthat the electrical resistance of the top soda lime layer was millionohms and the lower soda lime layer had a resistance of 6 million ohms.In testing such a canister in a 1 percent by volume of chlorine gas witha percent relative humidity at 250C, it was found that the electricalresistance of the bottom or lower soda lime layer progressivelydecreased. However, the resistance decreased quite slowly at first andthen decreased much more rapidly so that after a period of approximately22 minutes, the resistance was 80,000 ohms. After 33 minutes, theresistance was still further reduced to 24,000 ohms, and at 38 minutes,the resistance was reduced to 9000 ohms. The circuitry for the alarmdevice was such that the lamp was energized to give a warning of thetype hereinbefore set forth. As pointed out above, the alarm device canbe preset to any desired value of chemical resistance which would beproportional to the amount of advance warning required by the user.

Another canister which was tested was identified as a L .1 0 s s sts l qby. M ssiafs y An.

pliance under Model GMC and consists of a mixture of activated charcoaland soda lime. The electrode was inserted in this mixture which had anelectrical resistance of 4 million ohms. After using the canister in abreathing chamber containing 1 percent by volume of chlorine and 65percent relative humidity at 25C. for a period of 38 minutes, it wasfound that the electrical resistance began to drop markedly and after 54minutes, the resistance had dropped to approximately 13,000 ohms whichcaused the lamp to be energized.

Another canister was the Mine Safety Appliance Model GMD-SS used forprotection against ammonia gas and organic amines and fog. Silica gelwas used as a chemical sorbent. The initial electrical resistance of theanhydrous silica gel was approximately 200 million ohms. On use of thecanister in an atmosphere containing 2% percent by volume of ammonia ina relatively moist atmosphere having a relative humidity of percent at atemperature of 20C., the resistance decreased slightly for approximately55 minutes.

As the moisture and ammonia gas progressed through the silica gel andreached the exposed portion of the electrode in the silica gel sorbent,the electrical resistance began to drop markedly. After approximatelyminutes, the electrical resistance dropped to about 340,000 ohms whichcaused the warning lamp to be energized.

Satisfactory operation of the warning device was also obtained using itwith a rocket propellant canister such as the type GMN-SSW of MineSafety Appliance Company. The rocket propellant canister affordsprotection against nitric acid, dimethyl hydrazine, hydrazine, andhydrogen peroxide. Each canister contains the following layers ofchemical sorbents: a top layer of activated charcoal, a middle layer ofsilica gel, and a bottom layer of soda lime. This canister is equippedwith a window indicator and is manufactured by Mine Safety Appliance Co.

The electrode rod (8 gauge) was inserted from the canister top into thesoda lime layer. The polymer insu lation was removed from two portionsof the electrode rod. The lower electrode portion was exposed to thesoda lime layer over a length of three-fourths inch from its tip. Thepolymer insulation was also removed from the upper portion of this sameelectrode over a length of one inch and exposed to the silica gel layer.The electrical resistance of the soda lime layer was measured to be 100million ohms and that of the silica gel layer was 500 million ohms.

A small breathing chamber containing a simulated rocket propellantatmosphere consisting of 1 percent (by volume) of nitric acid vapor, /2percent hydrazine, and 0.05 percent aniline and having a relativehumidity of 70 percent at C. was inhaled into the canister, equippedwith our visual warning device, preset to a sorbent resistance warningvalue of 150,000 ohms. On continued inhalations, the electricalresistance of the soda-lime layer remained essentially unchanged for aperiod of about 20 minutes. Thereafter, as the vapors progressedthroughout the soda-lime layer, the electrical resistance decreased.After minutes, the electrical resistance of the soda lime was 30 millionohms and that of the silica gel was still high at 300 million ohms.After a period of 50 minutes of inhalations, the resistance of thesilica gel began to drop.

At the end of 120 minutes, the canister was approaching exhaustion inthis gaseous chamber. The electrical resistance of the sodalime layerwas about 150,000 ohms and that of the silica gel was about 1 10 millionohms. The visual alarm device was then activated, as determined bypreset electrical resistance values in the chemical sorbent layer.

The above examples are representative of what results can be obtainedwith canisters of this type.

It should be appreciated that in connection with the foregoing inventionthat the chemical breathing apparatus can be checked while it is instorage. in particular, the condition of the chemical sorbents in theoxygen generating canisters and in the gas mask filter canisters can bechecked merely by measuring the value of the electrical resistancebetween the electrodes. Assuming that the electrode has been insertedduring manufacture, this test can be accomplished readily and easily soas to make sure that the canisters are all in good condition and readyfor use by firemen and the like.

Although the present invention has been described primarily inconnection with humans, it should be appreciated that, if desired, thesame principles can be utilized for breathing apparatus for animals suchas dogs and horses.

it is apparent from the foregoing that there has been provided a new andimproved chemical breathing apparatus with an electrically actuatedalarm device which is particularly adapted for use with various chemicaltype canisters for giving an indication as to when only a certainpredetermined effective time remains for use of the canister. The alarmdevice will give an accurate indication even though the breathingapparatus may be used in steamy or water-saturated areas. The alarmdevice will still give an accurate indication even though the totaleffective life of the canister is greatly reduced because of the highconcentration of moisture in the air which is introduced into thecanister.

The warning device can be readily observed by the wearer and will give atrue indication as to how much longer the canister will be effective fortreating the gases introduced into the canister. it certainly is muchmore reliable than the color indicator which is difficult to read andcertainly difficult to observe during the time that the canister isbeing worn. The alarm device is directly responsive to the amount of airwhich passes through the canister. The screens which are utilized makepossible good contact with the chemical while still permitting the airto readily pass through the screen.

It should be appreciated that in the foregoing examples, the canisteritself was utilized as one of the electrodes. it should be appreciatedthat if it is desired to not use the canister one of the electrodes,additional electrodes can be placed within the canister to serve thisfunction. The alarm device can be utilized for checking the condition ofthe canister before it is used.

l claim:

1. In a chemical breathing apparatus with an electrically actuated alarmdevice for use by a human and adapted to supply life-sustaining gases tothe respiratory tract of the human who is operating in a gaseousenvironment, a canister adapted to be carried by the human, saidcanister containing at least one chemical sorbent through which gases tobe treated in the canister must pass, a face piece adapted to be placedover the face of the wearer and having communication with therespiratory tract of the wearer, means forming a fluid flow passagebetween the canister and the face piece so that treated gases which aretreated by the canister can travel to the face piece to be utilized bythe wearer, electrode means in contact with the chemical sorbent in thecanister and being in the form of spaced apart electrodes, one of saidelectrodes being positioned only in the upper portion of the chemicalsorbent so that the chemical sorbent disposed generally in the upperone-half portion of the canister presents a high resistance between theelectrodes, signalling means connected in series with the electrodes andmeans for applying a potential to the electrodes to give an indicationwhen the resistance of the chemical sorbent between the electrodes issubstantially reduced to thereby give an indication of the remainingeffective life of the canister.

2. A breathing apparatus as in claim 1 wherein said signalling meansincludes a lamp mounted on the breathing apparatus in a position whereit can be readily viewed by the wearer of the apparatus.

3. A breathing apparatus as in claim 1 wherein said canister is of thefilter type and is adapted to be opened to the atmosphere to permitatmospheric air to be drawn into the canister to be treated so that itcan be utilized by the wearer.

4. A breathing apparatus as in claim 1 wherein said chemical sorbent isprovided for generating oxygen and wherein said means establishingcommunication between the canister and the face piece include means forintroducing exhaled air into the canister where it is recirculatedthrough the canister to remove the carbon dioxide and to introduceoxygen so that the exhaled air can be reused by the wearer.

5. A breathing apparatus as in claim 1 together with means for testingsaid alarm device to see whether or not it is operative.

6. A breathing apparatus as in claim 1 wherein at lwats two differentchemical materials are utilized and in which chemical sorbents aredisposed in layers in the canister and wherein said first namedelectrode is disposed in one of said layers.

7. A breathing apparatus as in claim 1 wherein said alarm device isreadily detachable.

8 In a chemical breathing apparatus with an electrically actuated alarmdevice for use by a human and adapted to supply life sustaining gases tothe respiratory tract of the human who is operating in a gaseousenvironment, a canister adapted to be carried by the human, saidcanister containing at least one chemical sorbent through which gases tobe treated in the canister must pass, a face piece adapted to be placedover the face of the wearer and having communication with therespiratory tract of the wearer, means forming a fluid flow passagebetween the canister and the face piece so that treated gases which aretreated by the canister can travel to the face piece to be utilized bythe wearer, electrode means in contact with the chemical sorbent in thecanister and being in the form of spaced apart electrodes, one of saidelectrodes being positioned only in the upper portion of the chemicalsorbent so that the chemical sorbent presents a high resistance betweenthe electrodes, signalling means connected in series with the electrodesand direct current power supply means for applying a potential to theelectrodes to give an indication when the resistance of the chemicalsorbent between the electrodes is substantially reduced to thereby givean indication of the remaining effective life of the canister.

9. A chemical breathing apparatus as in claim 8 wherein said directcurrent power supply means is in the form of a battery.

10. In a chemical breathing apparatus with an electrically actuatedalarm device for use by a human and adapted to supply life-sustaininggases to the respiratory tract of the human who is operating in agaseous environment, a canister adapted to be carried by the human, saidcanister containing at least one chemical sorbent through which gases tobe treated in the canister must pass, a face piece adapted to be placedover the face of the wearer and having communication with therespiratory tract of the wearer, means forming a fluid flow passagebetween the canister and the face piece so that treated gases which aretreated by the canister can travel to the face piece to be utilized bythe wearer, electrode means in contact with the chemical sorbent in thecanister and being in the form of spaced apart electrodes so that thechemical sorbent presents a high resistance between the electrodes,signalling means connected in series with the electrodes and means forapplying a potential to the electrodes to give an indication when theresistance of the chemical sorbent between the electrodes issubstantially reduced to thereby give an indication of the remainingeffective life of the canister, said electrode means being in the formof one electrode extending into the chemical sorbent and the otherelectrode being in the form of a body with the chemical sorbent disposedin the body.

11. A breathing apparatus as in claim 10 wherein said first namedelectrode is in the form of a screen-like element disposed in thechemical sorbent.

12. A breathing apparatus as in claim 10 wherein said first namedelectrode makes electrical contact with two spaced layers.

13. A breathing apparatus as in claim 12 wherein said first namedelectrode is in the form of a pair of spaced, generally parallelscreen-like members which are connected in parallel and which aredisposed in separate spaced layers.

1. In a chemical breathing apparatus with an electrically actuated alarmdevice for use by a human and adapted to supply life-sustaining gases tothe respiratory tract of the human who is operating in a gaseousenvironment, a canister adapted to be carried by the human, saidcanister containing at least one chemical sorbent through which gases tobe treated in the canister must pass, a face piece adapted to be placedover the face of the wearer and having communication with therespiratory tract of the wearer, means forming a fluid flow passagebetween the canister and the face piece so that treated gases which aretreated by the canister can travel to the face piece to be utilized bythe wearer, electrode means in contact with the chemical sorbent in thecanister and being in the form of spaced apart electrodes, one of saidelectrodes being positioned only in the upper portion of the chemicalsorbent so that the chemical sorbent disposed generally in the upperone-half portion of the canister presents a high resistance between theelectrodes, signalling means connected in series with the electrodes andmeans for applying a potential to the electrodes to give an indicationwhen the resistance of the chemical sorbent between the electrodes issubstantially reduced to thereby give an indication of the remainingeffective life of the canister.
 2. A breathing apparatus as in claim 1wherein said signalling means includes a lamp mounted on the breathingapparatus in a position where it can be readily viewed by the wearer ofthe apparatus.
 3. A breathing apparatus as in claim 1 wherein saidcanister is of the filter type and is adapted to be opened to theatmosphere to permit atmospheric air to be drawn into the canister to betreated so that it can be utilized by the wearer.
 4. A breathingapparatus as in claim 1 wherein said chemical sorbent is provided forgenerating oxygen and wherein said means establishing communicationbetween the canister and the face piece include means for introducingexhaled air into the canister where it is recirculated through thecanister to remove the carbon dioxide and to introduce oxygen so thatthe exhaled air can be reused by the wearer.
 5. A breathing apparatus asin claim 1 together with means for testing said alarm device to seewhether or not it is operative.
 6. A breathing apparatus as in claim 1wherein at lwats two different chemical materials are utilized and inwhich chemical sorbents are disposed in layers in the canister andwherein said first named electrode is disposed in one of said layers. 7.A breathing apparatus as in claim 1 wherein said alarm device is readilydetachable. 8 In a chemical breathing apparatus with an electricallyactuated alarm device for use by a human and adapted to supply lifesustaining gases to the respiratory tract of the human who is operatingin a gaseous environment, a canister adapted to be carried by the human,said canister containing at least one chemical sorbent through whichgases to be treated in the canister must pass, a face piece adapted tobe placed over the face of the wearer and having communication with therespiratory tract of the wearer, means forming a fluid flow passagebetween the canister and the face piece so that treated gases which aretreated by the canister can travel to the face piece to be utilized bythe wearer, electrode means in contact with the chemical sorbent in thecanister and being in the form of spaced apart electrodes, one of saidelectrodes being positioned only in the upper portion of the chemicalsorbent so that the chemical sorbent presents a high resistance betweenthe electrodes, signalling means connected in series with the electrodesand direct current power supply means for applying a potential to theelectrodes to give an indication when the resistance of the chemicalsorbent between the electrodes is substantially reduced to thereby givean indication of the remaining effective life of the canister.
 9. Achemical breathing apparatus as in claim 8 wherein said direct currentpower supply means is in the form of a battery.
 10. In a chemicalbreathing apparatus with an electrically actuated alarm device for useby a human and adapted to supply life-sustaining gases to therespiratory tract of the human who is operating in a gaseousenvironment, a canister adapted to be carried by the human, saidcanister containing at least one chemical sorbEnt through which gases tobe treated in the canister must pass, a face piece adapted to be placedover the face of the wearer and having communication with therespiratory tract of the wearer, means forming a fluid flow passagebetween the canister and the face piece so that treated gases which aretreated by the canister can travel to the face piece to be utilized bythe wearer, electrode means in contact with the chemical sorbent in thecanister and being in the form of spaced apart electrodes so that thechemical sorbent presents a high resistance between the electrodes,signalling means connected in series with the electrodes and means forapplying a potential to the electrodes to give an indication when theresistance of the chemical sorbent between the electrodes issubstantially reduced to thereby give an indication of the remainingeffective life of the canister, said electrode means being in the formof one electrode extending into the chemical sorbent and the otherelectrode being in the form of a body with the chemical sorbent disposedin the body.
 11. A breathing apparatus as in claim 10 wherein said firstnamed electrode is in the form of a screen-like element disposed in thechemical sorbent.
 12. A breathing apparatus as in claim 10 wherein saidfirst named electrode makes electrical contact with two spaced layers.13. A breathing apparatus as in claim 12 wherein said first namedelectrode is in the form of a pair of spaced, generally parallelscreen-like members which are connected in parallel and which aredisposed in separate spaced layers.